For the budding science fiction writer: More local color

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The third in our sequence of posts for those who are starting to write science fiction.

So now you’ve picked your world and the star it circles.  You’ve figured out how far away it should be.  What should the world look like?  How can you make it distinct?

There are limitless ways in which you can pursue this.  Exotic fauna is one way: make the animals different from those on Earth.  We’ll explore this in an upcoming post.  I’m going to concentrate on the flora in this one: what should vegetation look like on your planet, assuming it has vegetation at all?

Flowers come in all shapes and sizes and colors.  The local quality of light may make some differences, but you are pretty much free to choose what you want in this regard.  However, leaf color is probably going to be determined by the star you’ve picked.

Stellar spectra

Light curves from three types of stars

The figure shows a schematic diagram, representative only,  of the spectrum of different classes of stars.  This shows the relative amounts of power which the star emits as a function of the wavelength of light.  Human eyes are insensitive to most light: our eyes are most sensitive in the wavelength region in which our sun emits the most light.

On Earth, leaves are green because Earthly chlorophyl absorbs blue (shorter wavelength) and red (longer wavelength) light predominantly.  Why this is so is a little bit tricky.  The chemical pathways by which plants absorb light and convert it into energy are complicated, and involve no less than about 8 photons per reaction.  Red light has low energy photons but can be used directly for photosynthesis.  Blue light has high-energy photons, but can be “down-converted” to lower energy to make them useful for photosynthesis.  Because of this, photons of wavelengths which appear blue and red to our eyes are used for photosynthesis on Earth and are absorbed, while middle wavelength photons, i.e., green light, is reflected,  leading to leaves being green.

Vegetation under different stars is probably going to look different.  Dr. Nancy Kiang and her colleagues at NASA have investigated the most likely chemical pathways for energy uptake for vegetation on planets circling other stars.  Note that the M-class star emits less light in toto than the sun does.  Dr. Kiang and her group theorized that plants on worlds circling M-class stars would need every available photon; if they absorb all light, they would appear black.  On the other hand, planets circling F-class or brighter stars would have too much light, especially in the short wavelength spectral region.  They might have to reflect the blue light, leading to blue-looking leaves.

These are just a few of the details which the science fiction writer needs to keep in mind.  In the next post, we’ll discuss how the distance of the planet determines the length of the year.

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